1. Field of the Invention
The present invention relates to indexing apparatuses and, more particularly, is directed to indexable apparatuses for selectively orienting objects such as workholding devices in precise predetermined positions.
2. Description of the Invention Background
A number of different apparatuses have been developed for indexing a variety of articles between manufacturing operations to increase the efficiency of the manufacturing process. For example, various types of indexing apparatuses are typically used to accurately present a workpiece in a predetermined orientation relative to the spindle of a machining device such as a milling machine or the like.
One type of such indexing device is disclosed in U.S. Pat. No. 2,339,986 to Engert. The device in that patent comprises an indexable device for indexing a shaft into a variety of different machining orientations about a single axis. While this device advantageously can support a shaft in various orientations to enable, for example, keyways to be cut in different locations on the shaft, the device can only hold a single shaft at a time and is ill-suited for supporting non-cylindrical workpieces.
Another indexable device is disclosed in U.S. Pat. No. 3,020,998 to Webb. That device comprises a turntable adapted to be indexed by the cyclic operation of a ratchet and pawl mechanism. A plurality of vise-like workholders are supported on the table and are adapted to be indexed about an axis such that the workholders can be positioned in various orientations relative to metal bending or crimping apparatus. This device, however, can only support workpieces in single planar orientations about the device's axis. Moreover, the ratchet and pawl system cannot be used to index the workholders to very precise and minute different angular orientations.
U.S. Pat. No. 2,369,425 to Becker discloses an indexable workholding device that comprises a frame that is adapted for attachment to the machining table of a machining device such as drill press. A disk is rotatably attached to the frame and may be rotated about an axis and secured in a predetermined position by clamping members attached to the frame. The top of the disk is also configured to accept workpiece holding clamps thereon. The outer edge of the disc is provided with a vernier scale that cooperates with an indicator on the frame to very precisely indicate the rotational position of the disc relative to the frame. The workpiece accuracy is dependent upon the upon the secure clamping of the disk in position and the secure clamping of the workpiece on the disk. If either the workpiece or the disk moves even slightly, the workpiece accuracy will be compromised. A similar apparatus for retaining workpieces at selective angles is also disclosed in U.S. Pat. No. 2,406,043 to Sorensen. That device also comprises a rotatable plate member that is equipped with a plurality of threaded apertures adapted to receive workholding clamping members therein. Although this device is capable of indexing a workpiece at relatively precise angular orientations, if the clamping assemblies attaching the workpiece move, the workpiece accuracy is compromised.
All of the above indexing apparatuses have limitations. In particular, those apparatuses that can position an item or workpiece in a relatively accurate position are generally incapable of supporting the workpiece in a very accurate and rigid position when it has external forces, such as those typically generated by various machine tools, assembly apparatuses or other manufacturing devices applied thereto. Such indexing apparatuses that do provide an adequate degree of rigidity typically cannot achieve the desired positioning accuracy or they are expensive to manufacture and maintain.
A number of indexing apparatuses typically can only index items about a vertical or horizontal axis or they can only index items that are received or oriented in a common plane. Such indexing apparatuses are not well suited for use in those applications wherein it is desirable to present multiple surfaces of multiple workpieces to the spindle of a machining device. It will be appreciated that by indexing a workpiece relative to the spindle of a machining device, several workpiece surfaces typically may be machined without the necessity of removing the workpiece from the workholder and re-clamping it in other machining orientations.
One device that addresses this problem is manufactured by Chick Machine Tool, Inc. of 800 Commonwealth Drive, Warrendale, Pa. 15086 under the trademark "Multi-Lok". This devise comprises a vise-like clamping assembly that is equipped with first and second movable jaw supports to which first and second jaw members may be removably attached. A fixed center jaw is attached between the movable jaws to provide two workpiece holding stations. Multiple two-station clamping assemblies can be received on a common column member that has a plurality of slide receiving slots therein. A column supporting base plate can be selectively attached to end of the column to enable the column to be attached to an indexable workholding table and thus enable the column to be selectively rotated relative to the spindle of, for example, a horizontal CNC milling machine. Such device, however, relies on an indexing mechanism that is a part of the milling machine. As such, it cannot be used to index workpieces on other machining devices that are not equipped with such indexable support members.
Another multiple workholding device manufactured by Chick Machine Tool, Inc., under the trademark "Multi-Dex", is also well-suited for clamping and selectively indexing a plurality of workpieces within the machining envelope of a machining device. This workholding device, in general, comprises a column member that supports a plurality of vise-like clamping assemblies that are similar to the Multi-Lok assemblies described above. However, the column member has a base plate formed thereon or attached thereto that may be attached to a selectively indexable support apparatus. Examples of selectively indexable supports are disclosed in U.S. Pat. No. 4,991,463 and U.S. Pat. No. 4,884,474 both to Kawata. Such assembly can be automatically indexed without the aid of hydraulic or electrical power, simply by contacting an actuator member with the machining device's spindle or the machine tool that is attached thereto. When a single two-station workholding device is indexed, the two workpieces retained therein can be machined on three sides before they must be removed from the workholder. Because the workholders described immediately above provide means for indexing four two-station workholders, a total of twenty four machining sequences (two workpieces/workholder.times.three sides/workpiece yields six exposed sides for machining sequences.times.four workholders) can be performed before the workpieces have to be removed from the workholders to be reoriented if necessary. Such device therefore increases the machine operator's "walk away" time (i.e., the time the machine can advance through preprogrammed machining sequences without the aid of an operator to relocate or reposition the workpiece(s)) and, thus, increases the machining apparatus' efficiency. However, this device is adapted to be actuated by the machining apparatus itself and, thus, is not well adapted for manual actuation. Moreover, due to the types of gears used to lock the workholder in various angular positions, very precise accuracies of, for example, three arc seconds, cannot be achieved.
Thus, there is a need for an apparatus capable of indexing one or more items to very precise orientations about an axis that can also rigidly retain such items in that orientation when the items are under the influence of external forces.
There is a further need for an indexing apparatus that has the above-mentioned attributes that is relatively inexpensive to manufacture and maintain.
There is yet another need for an indexing apparatus that can be can be easily adapted to index items about a horizontal or a vertical axis.
There is a need for an indexable workholding apparatus that can selectively support a plurality of workpieces or workholders in very accurate angular orientations.
There is a further need for an indexable apparatus that can be easily used in connection with a variety of different machining apparatuses.